Ethylene polymerization



Jan. 2l, 1958 c. H. DALE ETHYLENE POLYMERIZATION Filed Nov. 27, 195sKPEKQQNW Im@ Hu.

1N V EN TOR. C arf/a Dale.

United, States Patent-.

ETHYLENE PLYNIERIZATION Clark H. Dale, Grith, Ind., assigner to StandardOil Company, Chicago, Hi., a corporation of Indiana Application November27, 1953, Serial No. 394,542

18 Claims. (Cl. 260-94.9)

This invention relates to an improved process of polymerizing ethyleneand has particular reference to a process for the preparation ofnormally solid polymers of ethylene. By normally solid polymers ofethylene iS meant those polymers of ethylene which are capable ofindependent shape retention at 20 C. and atmospheric pressure. In oneaspect, this invention relates to a process for the manufacture ofpolyethylenes having crystallization or softening temperatures aboveabout 100 C. and specific viscosities (X104) above about 5000, but whichmay extend to 15,000, 25,000, 50,000 or even more.

In the polymerization of ethylene to normally solid polymers, animportant and recurrent problem has been to provide means for theremoval of the solid polyethylenes from the reaction vessels, especiallyin processes where ethylene is subjected to continuous or owpolymerization. Various solvents or carrier liquids have been proposedfor use in such processes to prevent the accumulation of diiicultyremovable polymer in the polymerization reaction vessels and to carrythe polymer from the reaction vessels to one or more separation zones.It was found, however, that the solvent media or carrier liquidsadversely affected the polymerization reaction, sometimes entering intothe reaction and adversely affecting the properties of the polymer(note, for example, United States Patent No. 2,475,643). Pure water doesnot appear to enter into reaction with ethylene during thepolymerization, but it has been found that the suspending capacity ofwater for normally solid polyethylenes is limited and it is ditiicult toattain long, continuous ethylene polymerization operations in thismedium. Only a few out of many organic compounds which were tested asreaction media for ethylene polymerization have proved to be useful.Sometimes the inutility of the various organic compounds was due toundesirable physical properties, for example, relatively high meltingpoint or very high boiling point, or tenacious retention by the solidpolyethylene; sometimes it was due to undesirable chemical propertiessuch as selective reaction with the catalyst or interaction with thegrowing polymer chain, and sometimes to factors which cannot be readilydefined but which were reflected in decreased polymer yield,unsatisfactory suspending power for the solid polyethylenes or the like.

A primary object of the present invention is the provision of animproved process of ethylene polymerization in a liquid medium processin which an easily recovered granular polymer is produced. Anotherobject of this invention is the provision of a novel carrier liquid forethylene polymerization that, serving as a reaction medium, will notinterfere with the course of reaction, but which also will provide apolymer having commercially suitable characteristics, particularlytoughness and flexibility. A further object of the invention is theprovision of a liquid reaction medium for ethylene polymerization thatcan be readily separated from the ethylene polymer. Yet another objectof the invention is the pro- 2,820,779 Patented Jan. 21, 1958 ricevision of a liquid reaction medium for ethylene polymerization that canbe separated from the ethylene polymer Without substantial alteration ofthe medium, so that it can be recycled to the reaction zone. Theinvention has for further objects such other advantages or results aswill be found in the specification and in the claims hereinafter made.

I have found that the foregoing objects can be accomplished and asuitable reaction medium or carrier liquid can be provided by supplyingto an ethylene polymerization zone either prior to the introduction ofethylene or in admixture therewith, neopentane, also termed2,2-dimethylpropane. Large proportions of neopentane, for example, 200%or more based on the Weight of reactant ethylene can be employed withoutinhibiting the polymerization reaction. Neopentane is effectivelyemployed in proportions between 10% and 200% by weight based on theethylene charged and preferably between 50% and The neopentane providesa medium in which ethylene is readily polymerized in the presence ofperoxide catalysts or other free-radical producing substances to formpolyethylenes having tough and flexible lms and a specic viscosity ofwell over 5,000 10-5; this latter value is a rough measurement ofmolecular weight and, sometimes, an indication of product suitability.

Neopentane has proved to be a liquid reaction medium and carrier liquidin which polyethylene forms in granules or similar small-sized,discreate shapes that can be readily separated from the remainder of thereaction mixture. If, in a continuous iiow system, the polymerization iseffected at temperatures Well above the softening temperature of thepolymer, usually from about l00-175 C., the polymer will be carried outof the reactor in the reaction medium. The polymer will then beprecipitated in a granular form upon cooling. It is preferred in someinstances to form the polymer at slightly below the softeningtemperature of the polymerized product.

A particularly surprising aspect of the invention is the fact that theuse of neopentane provides an ethylene polymer of high quality inreadily separable form whereas the use of its isomers, either n-pentaneor isopentane, resulted in both instances in the formation of brittle,unsuitable polymer which had to be dug out of the reactor. Furthermore,the use of isopentane and normal pentane at times results in conversionvalues of about halt' that obtained from neopentane.

The fact that only the neopentane isomer of pentane provides a goodproduct and is effective for polymer removal from the reactor suggeststhat neopentane is considerably more than a mere insert reaction mediumor carrier liquid and exerts a positive role in guiding thepolymerization or in effecting chain transfer or termination.

I prefer to employ substantially pure or concentrated neopentane,particularly anhydrous, deoxygenated neopentane. A commerciallyavaliable neopentane of 99% purity is especially suitable. Smallquantities, less than 5% by volume, of other liquid hydrocarbons, can beadmixed with the neopentane, particularly if a modification of theproduct is sought and if higher pressures within the disclosed range areemployed. Neopentane can be prepared by such means, for example, as thefractionation of neopentaue-containing petroleum products; or bypolymerizing butylene, hydrogenating the product, cracking thehydrogenated material, and fractionating the cracked product.

The use of free radical-producing substances as initiat'ors or catalystsfor the polymerization of ethylene to form normally solid polymers iswell known, having been described in numerous prior Letters Patent andother publications and does not per se constitute the present invention.Among the well known ethylene polymerization catalysts of the aforesaidtype, I may employ, for

3, example, oxygen or various inorganic peroxides such aspersulfate,lpercarbonate, pei-,berate and perchlorate salts of ammonia,the alkali metals and the` alkaline earth metals; various otherinorganic peroxides,'including hydrogen peroxide and various reactivemetal p eroxides such as zincperoxide, manganese dioxidefand the. like;`organic peroxides, including various diacyl peroxides such as acetylperoxide, benzoyl peroxide, lauroyl peroxide;

peroxides derived from carboxylic acids, for example, peracetic acid,persuccinic acid, their esters and the like; dialkyl peroxides such asdiethylperoxide, di-tert-butylperoxide and the like; ketone peroxidessuch as diacetone peroxide, methylethyl ketone peroxide, cyclohexanoneperoxide and the like; alkyl and cycloalkyl hydroperoxides such astert-butyl hydroperoxide, tetralin peroxide, pinane hydreperQXideS,a1Pha-a1pha'dimethylbenzy1 hydroperoxide or the like; various organicnitrogen compounds, which are capable of producing free radicals attemperav tures between about 2,0l and about 300 C. at a desirable rate,including diazo compounds, derivatives of hydrazine, various azines,oximes, amine oxides, and certain azo compounds; various reactivehydrocarbon derivatives of metals such as alkyl and aryl compounds oftin, lead, the alkali metals, etc.; a miscellany otv other freeradicalproducing substances such as the so-called organic positivehalogen compounds (N-bromosuccinimide and the like), hexaphenylethane,hexachloroethane, etc.

Particularly desirable catalysts for employment in this invention aredi-peroxydicarbonate esters having the formula O n1-0b-oot|iou2 whereinR1 and R2 represent organic radicals, for example alkyl radicals such asmethyl, ethyl, propyl, nbutyl, isobutyl, tert-butyl, amyl and the like,or different types ofA organicV radicals (note, for example, USP

Dialkyl peroxides having the'formula RlOORbwhe'rein R1 and R2 may be thesame or different, are also especially desirable from the practicaloperating standpoint. A third class of free radical-producing substanceswhich function extremely well as catalysts f orthe poly-` merization of'ethylene to normally solid polymers are the alpha-alpha-azo-bis-isoalkylnitriles having the general formula Y wherein R1 and R., are alkylgroups and Rzand' R3 are t @sangra alkyl, cycloalkyl, or aryl groups.VHowever, R1 and R2A v may be linked together as a carbocyclic ring, e.g. a cyclopentyl or cyclohexyl ring, andV this applies likewise t9 Reand Re vThe concentration of free radical-catalysts employedy in thepolymerization reaction may, in general, be-varied betweenabout 0.001and about 1% by weight,` based on the weight of the ethylene chargingstock, although more or less catalyst may be used, dependingupon4 thevrspecific operating conditions of time, temperature and rassure, solventconcentration, etc., the specificl character---Spartiti@-fleompcstieutemperatures@temperatureranges;

ofr` varitnisfree radical-producing substances have; been, published,vfor2 example, inA C. E. vSchildknecht,V Vinyl and Related; Bolyzners.ohn. Wiley audSons, Inc., Y2,

4 1952), page 78. The present invention is' not concerned withthespeciic temperature ranges for use with the various free radicalcatalysts since these are either well known in the art or can be readilydetermined by one skilled in the art through `routine experimentation. Iprefer to employ free radical catalysts which can be used in thetemperature range of about 20 C. to about 300 C.,

Ypreferably about 40 C. to about 200 C.

The ethylene, polymerization pressure is selected in view of thefotherreaction variablesA and of the characteristics desired in the product.In general, increasing the partial pressure of ethylene in the reactionzone tends to increase the molecular weight of the polyethylene. Agenerally useful polymerization pressure range is between about 500 p.s. i. and about 30,000p. s. i., although even higher pressures may beused. The more frequently used pressure range isl between about 5000 andabout 15,000

a higher pressure can also bey employed, extreme elevations in pressurehave little eect on liquid phase polymerization. The organicperoxydicarbonate catalyst, which is` preferably adialkylperoxydicarbonate, is yernployed in amounts byweight based onethylene of between 0.005 and about 1 percent. Depending upon the otherreactionk Variables 'and upon the nature of the product desired, thepolymerization period may vary fromjless than about one-quarter toaboutfifty hours. Generally, the reaction rate will not vary materially withsmall variations in` pressure, the' Vlimiting rate apparently being therate of solutionV of ethylene in the neopentane, l However,-if theethylene. is introduced into the react-ion zone as al solution ofethylene in neopentane, increases; in

the partiel]` pressure ofethylene within the disclosed range ofv 50,0.to 30,000pounds and particularly Within the range ofL 500.to5,000pounds. per square inch may increase the rate of polymerization.

The dialkyl peroxides such as dimethyl, diethyl, di-npropyl,diisopropyl, di-tertiary butyl, methyl tertiary butyl, ethyl tertiarybutyl. peroxides, and. the like can be employed at temperatures withinthe range of about 60"` C. toabout, 300.? C. However, temperatures above200 C. are` employed. only with the more stable members ofthe dialk-ylperoxide seriesand/ or at high ethylene pressures ofabout 15,000 p.,s.`i. or more.

The. alpha-alphaf-azo-bis-isoalkyl nitriles, and the ,correspending`cycloalkyl nitriles are usually employed, at temperatures, withintherange of about 35 C. to about C.; It, willbeunderstood that it is well,within the` skillof the. art to determine the optimum speciiicltemperatures. to, employ with a given catalyst and a given objectiveintheway of product-properties.

The, reaction can,Y be,y performed either continuouslyl or batchwise.Continuous reaction vessels cancontaintube bundles; or. maybe providedwith other conventionalcooling means. YThe, reactors Vshould bestainless steel or some, other corrosion-resistant; alloy. ln, a tlowreactor, ethylene` can-be introduced in solution in neopentanevorseparately. andI be caused to flow into contact withk the' catalystwhich1 can beinuoduced with the ethylene, meenemen@ or; otherwise.

VWitte reaetiongis, completed, the resultant slurry ot polymerneopentane,canA be cooled to a temperature beIQML- 9;5,1AC.,.he.boilingpoint of neopentanmvand Ythe imposedpressurecanathen bereduced so that unreacted ethylene can be' flashed ol and recycled.Alternatively,` the-pressureiover-the hot reaction-'product canV bereduced@ 45 and vaporized ethylene and neopentane can be flashed fromthe polymer and, preferably, be recycled. The polyethylene-neopentaneslurry obtained by the first men- Vtioned method, can either bespray-dried or the neopentane can be allowed to flash oi in some othersuitable manner. The product obtained is free-flowing and granular.

Reference will now be made to the accompanying ligure which illustratesone embodiment of the present invention. The ethylene charging stock canbe prepared by a variety or" methods known in the art. Thus, ethylenemay be obtained from petroleum refinery gas streams, e. g. streamsderived from thermal or catalytic cracking processes, from hightemperature cracking of propane, by catalytic dehydrogenation of ethane,by treatment of ethane-oxyge'n mixtures at high temperatures, bycatalytic dehydration of ethanol and the like. The ethylene streamsubjected to polymerization should be substantially tree of oxygen andsulfur or their compounds, and free of nitrogen compounds. lll/'hen thepolymerization catalyst is not oxygen, l prefer to employ ethylenecharging stocks containing 10 parts by weight per million of molecularoxygen or less. The charging stocks should contain no sulfur or nitrogencompounds and at most only small proportions of higher olens such aspropylene or butylenes. Molecular oxygen exerts a remarkable retandanteiectupon other free radical-producing polymerization catalysts such asperoxydicarbonate esters. such that cornmercial cylinder ethylenecontaining in the neighborhood of 0.05 weight percent of molecularoxygen is unsuitable as a feed` stock for the present polymerizationprocess. Propylene concentrations of the order of about 0.5 weightpercent in the ethylene charging stock can be tolerated when theethylene is to be polymerized to polyethylenes having a softening pointabove about 100 C., but it has been observed that higher concentrationsoi propylene, for example, about percent, or more in the ethylenecharging stock, markedly reduce the softening point of the polymer whichis produced by the process of the present invention. Propylene andhigher oletlns may be selectivelyiremoved from ethylene by adsorption,polymerization, alkylation, etc. v l The charging stock employed in theprocess or" this invention may contain saturated hydrocarbons such asethane and propane, which exert a diluent eect by reducing the amount ofethylene in the polymerization zone, butjdo not exert any poisoning eecton the polymerizatin reaction.

illustrated, ethylene is passed from source 1i) through apump orcompressor 11 and heater 12 into a puriiier indicated schematically at13. In zone 13, oxygen, and litrogen and sulfur-containing materials areremoved from the ethylene stream. Prior art processes for the removal ofsmall amounts of oxygen from hydrocarbon gas streams may be employed forthe purpose of deoxidizing the ethylene charging stock. By Way ofexample the ethylene 'may be deoxidized after being compressed to 750 p.s. i. g. and heated toabout 150 C. by passage through a column packedwith grains of metallic copper. An alternative lmethod of deoxidizingcomprises contacting the ethylene, under desired pressure, with analkali metal or an alkaline earth metal, for example, molten sodium or asodiur.- potassium alloy. The oxygen content of ethylene is readilyreduced below parts per million by contacting it with molten sodiumalloys at temperatures of about 125 C..to about 150 C. over a period ofabout 1/2 to 'about 12 hours. Other suitable methods of oxygen removalare described in British Patent No. 560,497. lt may be desirable toremove oxygen and sulfur compounds from Yethylene by different methodsin separate zones..

From the puriiier 13, the ethylene charging stock is passed through aheat exchanger 14 wherein the ethylene is brought to a desiredtemperature. rfhe heated ethylene 'iis-'compressed to the selectedpolymerization pressure by compressor 15 and is pumped thereby throughline 16 into reactor'19. l

Neopentane is pumped from a source 17 to polymerization pressure andinto line 16 by pump 18. As shown, the neopentane mixes with theethylene charging stock in line 16, but the neopentane and ethylene canbe separately charged to the reactor.

The polymerization catalyst is pumped through line 20 from a source 21by a pump 22 and is delivered, preferably in solution or dispersion inneopentane, introduced through valved line 23, into the said line 2i).The catalyst can also be injected into the reactor 19 dispersed in anyinert liquid hydrocarbon.

In reactor 19, ethylene is polymer-ized. The reactor can be providedwith internal cooling coil 24, through Which a heat transfer medium canbe circulated to aid in controlling the temperature during theexothermic/etbylene polymerization reaction. The reactor can be made ofstainless steel, aluminum or its alloys, or be lined with glass, silver,nickel, or tin. v

The dispersion of ethylene polymer in the neopentane in the bottom ofthe reactor, which dispersion may be maintained by a mechanical mixingdevice (not shown), leaves the reactor by line 2S which may be providedwith a steam jacket (not shown) although when the usual proportions ofneopentane are employed,vthe jacket is not necessary. TheV dispersedpolyethylene passes through a valve 26 which can be conventionallycontrolled by the level of liquid in the reactor. Y

Neopentane, polyethylene, and unreacted ethylene can be recycled throughvalved line 27 by pump 28 and be passed thereby through heat exchanger29 which can aid in controlling the temperature of the exothermicpolymerization.

Another portion of the dispersion of polyethylene 'in neopentane or eventhe total output of the reactor 19 can be passed through a cooler 3l) inwhich it may be cooled to a temperature below 9.5 C., the normal boilinglpoint of neopentane. The cooled dispersion is then owed through valve31, whereby the pressure is reduced to the extent that substantially thetotal content of unreac'ted ethylene will flash ofi the dispersion in aflash separator 32 into which it passed from the valve 31.

The separated ethylene can be recycled by pump 33 through valved lines34 and 3S or 35 into the ethylene charging stock preferably at a pointahead of the purifier 13 so that any impurities which may haveaccumulated in the Aethylene decomposition of catalyst in the reactorcan be removed.

Polyethylene slurry leaves the separator 32 through a valved line 37,flows through valve 3S therein, and enters evaporator S at aconsiderably reduced pressure. Heat can be supplied to the evaporator bycoil heater 40 or preferably by heat interchange with the cooler 3G.Neopentane is separated from the neopentane-polyethylene dispersion inthe evaporator 39, is owed through line 5i and cooler or condenser d2,and is recycled by pump 43 through the line 4l to the source i7 ofneopentane, and ultimately to the reactor 19.

Polyethylene can be removed by any conventional means 44 from theevaporator 39.

As an alternate manner of operation, polyethylene dispersed inneopentane can be removed from the reactor 19 and released frompolymerization pressure before cooling by iiowing the same through valve26 directly into flash separator 32. Both the neopentane and unreactedethylene will then flash from the polyethylene and the mixed vapors canbo recycled by pump 33 to the reactor 19.

The following speciiic examples are presented to illustrate the presentinvention.

Example 1 A stainless steel bomb having 330 cc. capacity was chargedwith 114 grams of ethylene, 135 cc. (about 83 grams) of neopentane of99% purity, and 0.054'cc. of diethylperoxydicarbonate. The charged bomb.was heated for 4 hours at 55 C. under an average pressure of 9000pounds per square inch gauge. The gaseous contents of the bomb were thenvented to the atmosphere and were cooled at room temperature. Unreactedethylene and neopentane evaporated from the bomb contents. A coarsegranular polyethylene product remained in the reactor and this flowedfreely from the bomb when it was inverted; the polyethylene, withoutfurther treatment, was substantially free of neopentane. A yield ofpolyethylene of 12.1 grams, representing a conversion of 10.5%, wasobtained. The product had a specific viscosity of 14,600X -5 and filmsprepared from it were tough and flexible.

When equal weights of isopentane and ethylene were heated for 4 hours atabout 55C., in the presence of 0.0505 grams of diethylperoxydicarbonateand at an average pressure of 6700 pounds per square inch gauge, aconversion of only 5.4% was obtained. The product was dicult to removefrom the reactor, was very brittle and had the unsatisfactorily lowspecific viscosity of 2600 105. When the experiment was repeated at 7800pounds per square inch gauge, using, instead of isopentane, an equalweight of normal pentane, the polymer again had to be mechanicallyremoved from the reactor and it was found to be brittle.

Example 2 The same reactor bomb as that 'of Example 1 was used and to itwere charged 99 grams of ethylene, an equal weight of 99% pureneopentane and 0.05%, based on the weight of ethylene charged, ofdiethylperoxydicarbonate. The bomb contents were heated at 55 C. for 4hours under an average pressure of 7330 pounds per square inch gauge.The bomb was Vented and the produced polyethylene, weighing 9.1 gramsand being equivalent to a 9.2% conversion, was easily recoveredtherefrom. The polymer yhad a specific viscosity of 10,800X105 and itformed tough and flexible film.

The foregoing examples illustrate particularly the advantages peculiarto neopentane in ethylene polymerization. The polymer obtained in bothinstances was granular in form and was easily removed from the reactor;it formed strong and exible films and had a molecular weight of at leastover 20,000 in the rst case and over 15,000 in the second.

Example 3 A 180 ml. stainless steel autoclave was charged with 75 ml. ofneopentane and 0.03 g. of di-tert-butylperoxide,

cooled to -100 C., flushed with hydrogen and evacuated, after whichethylene was condensed into the reactor in the amount of 70 g. Theautoclave was placed in a rocker apparatus and heated to 149 C.,atotding initial ethylene pressure of 8800 p. s. i. Reaction wascontinued for 3 hours to convert 22 w.% of the ethylene charge into avery tough and flexible polymer having a specic viscosity 10-5 of 6400,melt viscosity of 2.9 103 poises, and density (24/4) of 0.9234. Thecrystallization temperature of the polymer was found to be 105 C. byplacing a sample of the polymer between glass slides, heating on aMaquenne block to obtain clear, molten polymer and cooling slowly untila haze (due to crystal formation) appeared in the melt.l

In a parallel operation in which isopentane was employed as the reactionmedium, a markedly inferior polymer was produced which was more dicultto remove from the reactor. In this operation the autoclave was chargedwith 78 ml. of isopentane, 0.03 g. of di-tertbutylperoxide and 69 g. ofethylene and reaction was reffected at 149 C. for 3 hours. The initialethylene ethylene polymer was converted, the polymer was very brittleand had a specific viscosity )(10-5 whichV was less than 3500, ra meltviscosityV somewhat below. 100 poises, and density (24/4) of 0.9207. Thecrystallization temperature of the polymer was 104 C. The markedlysuperior results obtained with the use of the neopentane reaction mediumare readily apparent.

Example 4 The operating procedures and equipment were generally the sameas in Example 3,but involved the use ofalpha-alphaazobis-isobutyronitrile. The reactor was charged with 70 ml.of neopentane, 0.05 g. of the nitrile catalyst and 62 g. of ethylene.Reactionwas eected at 100 C. for 3 hours, starting with an initialethylene partial pressure of 8000 p. s. i. Of the ethylene charge, 18.6w. percent was converted into a exible polymer which was readilyYremoved from the autoclave. polymer had a specific viscosity 105 of4300, melt viscosity of 200 poises, and density (24/4) of 0.9306. Thecrystallization temperature of the polymer was 106 C. Y

In a parallel operation in which isopentane was employed as the reactionmedium, markedly inferior yresults were obtained. The autoclave wascharged with ml. of isopentane, 0.05 g. ofalpha-alpha'-azo-bis-isobutyronitrile and 70 g. of ethylene.Polymerization was effected at C. for 3 hours, starting with an initialethylene partial pressure of 8500 p. s. i. Of the ethylene charged, 16.5w. percent was converted to a brittle polymer having a specificviscosity 10-5 below 3500, melt viscosity of less than 100 poises, andc1424 of 0.9379. The crystallizaf tion temperature of the polymer was112 C.

In carrying out the above examples extreme precautions were observed toobtain pure reagents and to prevent the intrusion of impurities such asoxygen, carbon dioxide, and moisture during loading of the autoclave andduring reaction.

By the term specific viscosity I mean (relative viscosity-l), whereinrelative viscosity is the ratio of the time of elux of a solution of0.125 g. of polymer in 100 cc. of C. P. xylenes at 110 C. from aviscosimeter to the time of elux of 100 cc. of C. P. Xylenes at the sametemperature. The melt viscosity was determined by the method of Dienesand Klemm, l'. Appl. Phys. 17, 458l71 The polyethylenes produced by theprocess of this` invention can be subjected to such after-treatment asmay be selected, to fit them for particular uses or to impart desiredproperties. Thus ythe polyethylenes ycan be eX- truded, mechanicallymilled, or cast. Anti-oxidants, lillers, extenders, plasticizers,pigments, etc. can beincorporated in the polyethylenes. n

This application is a continuation-impart of my previous application,Serial No. 262,877, filed December 21, 1951, now abandoned.

Having thus described my invention, I claim:

1. A process which comprises passing ethylene into contact with acatalyst having the formula presence of at least 10 percent by weight,based on the ethylene charged, of a reaction medium consistingessentially of neopentane at a polymerization temperature ,between about20 C. and 100 C. and at a pressure between about 500 and about 30,000pounds pervsquare inch gauge.

2. The process of claim 1 wherein the relatlve quantity of neopentane isbetween l0 and 200 percent based on partial pressure was 8400 p. s. i.While 22 w.%` ot the 75 the Weight of reactant ethylene.

The y 3. The process of claim 1 in which the catalyst isdiethylperoxydicarbonate.

4. The process of claim 1 in which the catalyst isdiethylperoxydicarbonate and constitutes from 0.005 to 1 percent byweight of the ethylene.

5. A process of polymerizing ethylene which comprises introducingethylene into a reaction zone under such pressure as to maintain thereinan ethylene partial pressure of between about 2000 and 30,000 pounds persquare inch gauge, introducing also into said zone between 50 and 150percent by weight, based on the ethylene, of a reaction mediumconsisting essentially of neopentane, eiecting polymerization of theethylene at a temperature between about 20 C. and 100 C. and in thepresence of 0.005 to about 1 percent by weight, based on the ethylene,of diethylperoxydicarbonate, and obtaining a slurry of product polymerand neopentane, Vaporizing neopentane, and separating it from productpolymer.

6. The process of claim 5 in which the slurry is removed from thereaction zone, the pressure over the slurry is then reduced tosubstantially atmospheric pressure, and the neopentane contained in theslurry is llashed therefrom.

7. The process of claim 5 in which the slurry is removed from thereaction zone, is cooled to a temperature below the boiling point of theneopentane, and is thereafter released to a zone of reduced pressure,and in which process unreacted ethylene contained in the slurry isflashed therefrom in the said zone of reduced pressure and is recycledto the reaction zone.

8. A process of polymerizing ethylene which comprises introducing7ethylene into a reaction zone under such pressure as to maintain thereinan ethylene partial pressure betwen about 2000 and 30,000 p. s. i. g.,introducing also into said zone at least about 10 percent by weight,based on the weight of the ethylene, of a reaction medium consistingessentially of neopentane, effecting polymerization of the ethylene at atemperature between about 20 and 100 C. in the presence of a catalysthaving the formula in which R1 and R2 are alkyl redaicals, at atemperature between about 20 and 100 C., and a pressure between about500 and 30,000 p. s. i. g., the improvement which comprises employingwith the ethylene a polymerizationreaction medium consisting of at leastabout 10 percent by weight of neopentane, based on the weight of theethylene.

10. In a process for the preparation of a normally solid polymer bycontacting ethylene with a free radicalproducing polymerization catalystat a suitable temperature within the range of about 20 C. to about 300C. at which said catalyst decomposes substantially to form free radicalsand at a polymerization pressure of at least about 500 p. s. g. andsuiciently high to induce substantial polymerization., the step ofeffecting said contacting in the presence of a reaction mediumconsisting essentially of neopentane in a proportion of at least about10 weight percent, based on the ethylene.

l1. The process of claim 10 wherein the proportion of neopentane isbetween about l0 and about 200 weight percent, based on the weight ofethylene.

12. The process of claim 10 wherein said catalyst is analpha-alphaazobisisoalkyl nitrile.

13. The process of claim 10 wherein said nitrile isalpha-alpha'-azo-bis-isobutyronitrile.

14. The process of claim 10 wherein said catalyst is an organicperoxide.

15. The process of claim 10 wherein said catalyst is a dialkyl peroxide.

16. The process of claim 15 wherein said peroxide is di-tertiary butylperoxide.

17. The process of claim 14 wherein said peroxide is adi-peroxydicarbonate ester.

18. In a process for the preparation of a normally solid polymer bycontacting ethylene with a free radicalproducing polymerization catalystselected from the group consisting of a dialkyl peroxide, adi-peroxydicarbonate ester and an alphaalphaazobis-isoalkyl nitrile andelecting said contacting at a sutable temperature within the range ofabout 20 C. to about 300 C. at which said catalyst decomposessubstantially to form free radicals and at a polymerization pressure ofat least about 500 p. s. i. g. and suciently high to induce substantialpolymerization, the step of eiecting said contacting in the presence ofa reaction medium consisting essentially of neopentane in a proportionof at least about 10 weight percent, based on the ethylene.

References Cited in the le of this patent UNTTED STATES PATENTS2,405,962 Larson Aug. 20, 1946 2,728,753 Russum etal. Dec. 27, 1955

1. A PROCESS WHICH COMPRISES PASSING ETHYLENE INTO CONTACT WITH ACATALYST HAVING THE FORMULA